1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus for use in a copying machine, a laser printer, or the like.
2. Description of the Related Art
A developing device or an image forming apparatus of this type is disclosed in Japanese Laid-Open Patent Publication No. 3-101784 and Japanese Laid-Open Patent Publication No. 3-282488.
FIG. 12 shows an image forming apparatus disclosed in Japanese Laid-Open Patent Publication No. 3-101784. As shown in FIG. 12, this image forming apparatus has a hopper 309 for accommodating a toner. The hopper 309 is positioned behind a developing sleeve 308 in the vicinity of a photosensitive body 301. The toner in the hopper 309 is starred by a toner stirrer 311 provided An the hopper 309, scraped up to a toner supply hole 309a disposed on the side of the developing sleeve 308, end supplied to the developing sleeve 308 via the toner supply hole 309a. The developing sleeve 308 carries a supplied toner on its surface. After the thickness of the toner is regulated by pressure of an elastic blade, the toner is opposed to the surface of the photosensitive body 301 which has been exposed to light, and an electrostatic latent image formed on the surface of the photosensitive body 301 is developed with the toner.
The hopper 309 for accommodating the developer occupies a large portion of the developing device 303. Therefore, the diameter of the developing device 303 can be shortened only to a limited extent. As a result, an image forming section becomes a large one, together with the above developing device 303 and other numerous image developing elements disposed around the hopper 309. This is disadvantageous in arranging a compact apparatus required especially for personal uses.
Further, an image developing unit pulled out of the main body is handled in various positions, such as the axial line of the developing sleeve 308 is turned vertically, or the upper portion of the developing device 303 is inclined transversally or downwards.
On the other hand, as an image forming apparatus with a more compact body is popularly produced, the apparatus is not necessarily used in one specified position. In such a case, the developing device 303 is turned in various directions as above.
If the direction of developing device 303 is different in individual uses or handling, the density of developer particles becomes uneven.
That is, the particles of the developer concentrate in the lower side by the gravity effect, if the axial line of the developing sleeve 308 inclines or turns vertically, because the developer can move freely in the hopper 309 and about the developing sleeve 308.
If this is caused by a temporary handling, it is required to set the developing device 303 in a proper position so as to perform a smoothing drive so that developer particles extend evenly. Accordingly, an operator has to wait for the elapse of a stand-by time period.
Additionally, in the case of selecting the direction of setting a main body for continuous use, the problem of uneven developer is not solved. The developing efficiency is unstable depending on the direction of setting, which results in a poorly developed image or failure of development in some cases.
FIG. 13 shows an image forming apparatus disclosed in the Japanese Laid-Open Patent Publication No. 3-282488. The image forming apparatus has a circulating transporting path for transporting circularly the developer, behind a developing sleeve 402. The circulating transporting path comprises a developer transporting path 408 and a developer transporting path 409. The developer transporting path 408 is disposed along the developing sleeve 402. A toner supply path 420 extending from a hopper 417 located in a rear portion is connected with a part of the developer transporting path 409. Additionally, a screw which can hold the developer well is adopted as a developer transporting body in the circulating transporting path for distributing the developer circularly.
However, a large space is opened about the developing sleeve 402 in a portion facing the developing sleeve 402 of the circulating transporting path. Accordingly, a large idle space is formed between the screw and the developing sleeve 402 of the developer transporting path 408, where the developer can move freely without being held by the screw or the developing sleeve 402. In such a space, the particles of developer concentrate in the lower side depending on the changes of position of developing device, resulting in a poorly developed image or a failure of development.
Further, the developer once supplied in the developer circulating path from the hopper 417 is continued to be transported in the developer transporting path until it is used for development. This makes a part of developer deteriorate suddenly, which makes a stable development impossible. Also, in the case where the amount of developer consummation in a developing place differs extremely in one developing operation from another, the developer clogs in the course of developer circulating path.
In addition, the developer is poured into the hopper 417 from a developer refill container when the developer in the hopper 417 is used up. In order to refill the hopper with developer to continue the operation, the developer refill container is attached to the hopper, or a mouth of the developer refill container is put over a developer supply opening of the hopper 417. In this case, a stable development is possible only when the supplied developer reaches uniformly in the whole range of a portion along the developing sleeve 402, while being transported gradually in the developer transporting path. Accordingly, it is arranged to perform an initializing operation for driving the developing device for a predetermined time period after the developer is supplied.
However, in the above conventional method, the time period is needed for the initializing operation in addition to supply of developer. It is inconvenient for the operator to wait for the start of the image forming operation for the predetermined time period after the supply of the developer.